6 9 6 



CHEMISTR Y OF RESPIRA TION. 



water, no weighable amount of nitrogen, or of any other gaseous 

 substance, is discharged or absorbed by the animal. 



The figure below represents the modification of Pettenkofer's 

 apparatus, which was introduced by Voit for experiments on animals. 



The absorption of water is effected by flasks filled with pieces of 

 pumice saturated with sulphuric acid, and the carbon dioxide is in turn 

 absorbed by making the air bubble through a long tube filled with a 

 titrated solution of baryta. 1 



The advantages of Pettenkof er's method over those previously in use 

 are these It is possible, owing to the system of ventilation, to make 

 experiments upon man ; observations can for a similar reason be much 

 more prolonged without any danger of disturbance to the normal 

 respiratory exchange arising from an accumulation of carbon dioxide ; 

 the absorption of the carbon dioxide is more exact. Notwithstanding 

 these improvements, Pettenkofer's method possesses several disadvan- 

 tages and sources of error. The apparatus is complicated and costly, the 



FIG. 63. Volt's respiration apparatus. 



determination of the moisture is liable to be inexact, owing to deposition 

 on the walls of the chamber ; during the process of weighing the animal 

 there is an intake of oxygen, and an output of carbon dioxide and water, 

 which are not determined, and can only be calculated approximately ; 

 the absorption and estimation of carbon dioxide by the titration of the 

 baryta solution has been shown by Haldane and Pembrey 2 to be less 

 exact than it was thought to be. The result of these errors falls upon 

 the estimation of the intake of oxygen, for since 2 =C0 2 + H 2 w, it 

 is evident that the amount of oxygen may be often inexact. This has 

 been pointed out and proved by C. and E. Voit and Forster. 3 



It has already been mentioned that Voit 4 has constructed, upon 

 Pettenkofer's principle, a smaller apparatus for the determination of 



1 Baryta was first used by Pettenkofer for this purpose, but Dalton had previously used 

 titrated lime water. 



2 London, Edinburgh, and Dublin Phil. Mag., London, April 1890. 



3 Ztschr.f. BioL, Mtinchen, 1875, Bd. xi. S. 126. 4 Ibid., 1878, Bd. xiv. S. 57. 



